Many advanced missiles utilize a forward-facing optical sensor to guide the missile to its target. The sensor (or, equivalently for the present purposes, a portion of the optical train that directs the incoming optical rays from the scene to the sensor) is usually pivotably mounted so that the sensor may be directed to point in directions other than along the boresight axis of the missile. The sensor views the scene in front of the missile through a forward-facing window. The window protects the sensor from the high-velocity air stream and from ice, water droplets, and other solid or liquid particles that are present in the air.
In early high-velocity missiles, the window was typically shaped as a segment of a sphere. The sensor was effectively positioned at the center of curvature of the spherical window. In this arrangement, the sensor faced along a radius of the sphere at all pointing angles, so there was no distortion of the optical rays as a function of the pointing angle other than those due to imperfections in the window material.
The window is typically the most forwardly positioned element of the missile, and the spherical window shape can impose a significant aerodynamic drag on the missile. In more advanced missiles, the window is streamlined to reduce the aerodynamic drag, the non-spherical window being termed a “conformal” window. However, the use of the nonspherical, conformal window results in the optical rays reaching the sensor being distorted according to the pointing angle of the sensor.
Since the shape of the conformal window is largely determined by aerodynamic considerations, it cannot be significantly reshaped to reduce the angle-dependent distortion that reaches the sensor. The distortion can to some extent be compensated for computationally in the computer that processes the image. However, such distortion-compensation computations require large computing power and can interfere with the primary target recognition functions.
To reduce the distortion in the optical rays that reach the sensor, an optical corrector may be placed between the window and the sensor. The optical corrector has a spatially dependent shape that corrects the optical rays for distortions introduced as the optical rays pass through the window, as a function of the pointing angle of the sensor. The optical corrector thus functions somewhat in the manner of eyeglasses worn by a human being.
The existing optical corrector technology has worked well for the current generation of missiles. Conformal windows and appropriate optical correctors have been designed and developed responsive to the designs of the current missiles, and significantly improve their performance. Examples of such optical correctors are found in U.S. Pat. Nos. 5,946,143; 6,009,564; 6,028,712; 6,310,730; 6,313,951; 6,343,767; 6,462,889; and 6,552,318, all of whose disclosures are incorporated by reference.
However, further changes to the designs of future generations of missiles may require further adaptations to the window designs, and thence to the corrector designs. Conversely, improvements in window design and corrector design may permit improvements in missile design. There is accordingly a need for improved cooperative missile, window, and corrector designs that produce improved capabilities of the overall system. The present invention fulfills this need, and further provides related advantages.